Interferon: Types, Mechanism and Therapeutic Uses

Interferons (IFNs) are a family of signaling proteins belonging to the group of cytokines that are produced by various cells, particularly in response to viral infections.

They are named “interferons” because of their ability to interfere with viral replication as they inhibit or prevent viruses from multiplying inside host cells.

Interferons exert antiviral, antiproliferative, and immunomodulatory effects and act through autocrine and paracrine mechanisms.

They help limit viral infections by stimulating neighboring cells to express antiviral proteins and genes that inhibit viral replication.

Mechanism of Actions

Interferons can show their protective response through various mechanisms:

1. Inhibition of viral protein synthesis:
Interferons activate the enzyme Protein Kinase R (PKR), which inhibits protein synthesis by blocking the translation process. This prevents the formation of viral proteins.
2. Degradation of viral RNA:
Interferons activate the 2′,5′-oligoadenylate synthetase (OAS) pathway, which activates RNase L (Ribonuclease L). This enzyme degrades viral RNA and thereby inhibits viral replication.
3. Inhibition of viral replication:
Interferons stimulate the production of several antiviral proteins that interfere with different stages of viral replication, thereby restricting viral multiplication.
4. Activation of immune cells:
Interferons enhance the activity of natural killer (NK) cells and macrophages, helping in the elimination of virus-infected cells.
5. Induction of apoptosis:
Interferons can promote programmed cell death (apoptosis) in virus-infected cells, preventing further spread of infection.
6. Enhancement of antigen presentation:
Interferons increase the expression of MHC molecules, particularly MHC class I, which helps cytotoxic T-cells recognize and destroy virus-infected cells.

Classification and Functions of Interferons

Interferons (IFNs) are broadly classified into three main types based on their structure, receptors, and biological functions:

• Type I,

• Type II, and

• Type III interferons

Type I Interferons:

Type I interferons include IFN-α, IFN-β, IFN-ε, IFN-κ, IFN-ω and some other species-specific subtypes. Among these, IFN-α and IFN-β are the most important.

They play a major role in the early antiviral defence mechanism by inhibiting viral replication within host cells. They also help regulate immune responses, activate immune cells and induce apoptosis in virus-infected cells.

Type II Interferon:

Type II interferon is represented by IFN-γ (interferon-gamma). It is mainly produced by activated T-lymphocytes and natural killer (NK) cells in response to antigenic stimulation. Its primary function is to regulate immune responses and activate immune cells, particularly macrophages and NK cells.

It plays an important role in defending the body against intracellular pathogens and in antitumor immunity.

Type III Interferons:

Type III interferons include IFN-λ (interferon-lambda) and its subtypes. They provide antiviral protection mainly at mucosal surfaces, such as those of the respiratory and gastrointestinal tracts. They are produced primarily by epithelial cells and certain immune cells, including antigen-presenting cells.

Their antiviral activities are similar to those of Type I interferons, but their effects are mainly restricted to epithelial barriers, where they help prevent viral infection and maintain mucosal defence.

Activity Spectrum of Interferons

The different types of interferons work together as important signalling molecules to coordinate innate and adaptive immune responses and help the body control infections while maintaining an appropriate immune response.